package com.henushang.utils;

//Portions copyright 2002, Google, Inc.
//
//Licensed under the Apache License, Version 2.0 (the "License");
//you may not use this file except in compliance with the License.
//You may obtain a copy of the License at
//
//  http://www.apache.org/licenses/LICENSE-2.0
//
//Unless required by applicable law or agreed to in writing, software
//distributed under the License is distributed on an "AS IS" BASIS,
//WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
//See the License for the specific language governing permissions and
//limitations under the License.

//package com.google.gdata.util.common.util;

//This code was converted from code at http://iharder.sourceforge.net/base64/
//Lots of extraneous features were removed.
/* The original code said:
 * <p>
 * I am placing this code in the Public Domain. Do with it as you will.
 * This software comes with no guarantees or warranties but with
 * plenty of well-wishing instead!
 * Please visit
 * <a href="http://iharder.net/xmlizable">http://iharder.net/xmlizable</a>
 * periodically to check for updates or to contribute improvements.
 * </p>
 *
 * 
 * 
 * @version 1.3
 */

/**
 * Base64 converter class. This code is not a full-blown MIME encoder; it simply
 * converts binary data to base64 data and back.
 **/

public class Base64Util {
    /** Specify encoding (value is {@code true}). */
    public final static boolean ENCODE = true;

    /** Specify decoding (value is {@code false}). */
    public final static boolean DECODE = false;

    /** The equals sign (=) as a byte. */
    private final static byte EQUALS_SIGN = (byte) '=';

    /** The new line character (\n) as a byte. */
    private final static byte NEW_LINE = (byte) '\n';

    /**
     * The 64 valid Base64 values. made private and a method that returns a
     * clone can be added.
     */
    public final static byte[] ALPHABET = { (byte) 'A', (byte) 'B', (byte) 'C', (byte) 'D',
            (byte) 'E', (byte) 'F', (byte) 'G', (byte) 'H', (byte) 'I', (byte) 'J', (byte) 'K',
            (byte) 'L', (byte) 'M', (byte) 'N', (byte) 'O', (byte) 'P', (byte) 'Q', (byte) 'R',
            (byte) 'S', (byte) 'T', (byte) 'U', (byte) 'V', (byte) 'W', (byte) 'X', (byte) 'Y',
            (byte) 'Z', (byte) 'a', (byte) 'b', (byte) 'c', (byte) 'd', (byte) 'e', (byte) 'f',
            (byte) 'g', (byte) 'h', (byte) 'i', (byte) 'j', (byte) 'k', (byte) 'l', (byte) 'm',
            (byte) 'n', (byte) 'o', (byte) 'p', (byte) 'q', (byte) 'r', (byte) 's', (byte) 't',
            (byte) 'u', (byte) 'v', (byte) 'w', (byte) 'x', (byte) 'y', (byte) 'z', (byte) '0',
            (byte) '1', (byte) '2', (byte) '3', (byte) '4', (byte) '5', (byte) '6', (byte) '7',
            (byte) '8', (byte) '9', (byte) '+', (byte) '/' };

    /**
     * The 64 valid web safe Base64 values. made private and a method that
     * returns a clone can be added.
     */
    public final static byte[] WEBSAFE_ALPHABET = { (byte) 'A', (byte) 'B', (byte) 'C', (byte) 'D',
            (byte) 'E', (byte) 'F', (byte) 'G', (byte) 'H', (byte) 'I', (byte) 'J', (byte) 'K',
            (byte) 'L', (byte) 'M', (byte) 'N', (byte) 'O', (byte) 'P', (byte) 'Q', (byte) 'R',
            (byte) 'S', (byte) 'T', (byte) 'U', (byte) 'V', (byte) 'W', (byte) 'X', (byte) 'Y',
            (byte) 'Z', (byte) 'a', (byte) 'b', (byte) 'c', (byte) 'd', (byte) 'e', (byte) 'f',
            (byte) 'g', (byte) 'h', (byte) 'i', (byte) 'j', (byte) 'k', (byte) 'l', (byte) 'm',
            (byte) 'n', (byte) 'o', (byte) 'p', (byte) 'q', (byte) 'r', (byte) 's', (byte) 't',
            (byte) 'u', (byte) 'v', (byte) 'w', (byte) 'x', (byte) 'y', (byte) 'z', (byte) '0',
            (byte) '1', (byte) '2', (byte) '3', (byte) '4', (byte) '5', (byte) '6', (byte) '7',
            (byte) '8', (byte) '9', (byte) '-', (byte) '_' };

    /**
     * Translates a Base64 value to either its 6-bit reconstruction value or a
     * negative number indicating some other meaning.
     **/
    private final static byte[] DECODABET = { -9, -9, -9, -9, -9, -9, -9, -9, -9, // Decimal
                                                                                  // 0
                                                                                  // -
                                                                                  // 8
            -5, -5, // Whitespace: Tab and Linefeed
            -9, -9, // Decimal 11 - 12
            -5, // Whitespace: Carriage Return
            -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, // Decimal 14 -
                                                                // 26
            -9, -9, -9, -9, -9, // Decimal 27 - 31
            -5, // Whitespace: Space
            -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, // Decimal 33 - 42
            62, // Plus sign at decimal 43
            -9, -9, -9, // Decimal 44 - 46
            63, // Slash at decimal 47
            52, 53, 54, 55, 56, 57, 58, 59, 60, 61, // Numbers zero through nine
            -9, -9, -9, // Decimal 58 - 60
            -1, // Equals sign at decimal 61
            -9, -9, -9, // Decimal 62 - 64
            0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, // Letters 'A' through
                                                          // 'N'
            14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, // Letters 'O'
                                                            // through 'Z'
            -9, -9, -9, -9, -9, -9, // Decimal 91 - 96
            26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, // Letters 'a'
                                                                // through 'm'
            39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, // Letters 'n'
                                                                // through 'z'
            -9, -9, -9, -9, -9 // Decimal 123 - 127
    /*
     * ,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9, // Decimal 128 - 139
     * -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9, // Decimal 140 - 152
     * -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9, // Decimal 153 - 165
     * -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9, // Decimal 166 - 178
     * -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9, // Decimal 179 - 191
     * -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9, // Decimal 192 - 204
     * -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9, // Decimal 205 - 217
     * -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9, // Decimal 218 - 230
     * -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9, // Decimal 231 - 243
     * -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9 // Decimal 244 - 255
     */
    };

    /** The web safe decodabet */
    private final static byte[] WEBSAFE_DECODABET = { -9, -9, -9, -9, -9, -9, -9, -9, -9, // Decimal
                                                                                          // 0
                                                                                          // -
                                                                                          // 8
            -5, -5, // Whitespace: Tab and Linefeed
            -9, -9, // Decimal 11 - 12
            -5, // Whitespace: Carriage Return
            -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, // Decimal 14 -
                                                                // 26
            -9, -9, -9, -9, -9, // Decimal 27 - 31
            -5, // Whitespace: Space
            -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, // Decimal 33 - 44
            62, // Dash '-' sign at decimal 45
            -9, -9, // Decimal 46-47
            52, 53, 54, 55, 56, 57, 58, 59, 60, 61, // Numbers zero through nine
            -9, -9, -9, // Decimal 58 - 60
            -1, // Equals sign at decimal 61
            -9, -9, -9, // Decimal 62 - 64
            0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, // Letters 'A' through
                                                          // 'N'
            14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, // Letters 'O'
                                                            // through 'Z'
            -9, -9, -9, -9, // Decimal 91-94
            63, // Underscore '_' at decimal 95
            -9, // Decimal 96
            26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, // Letters 'a'
                                                                // through 'm'
            39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, // Letters 'n'
                                                                // through 'z'
            -9, -9, -9, -9, -9 // Decimal 123 - 127
    /*
     * ,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9, // Decimal 128 - 139
     * -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9, // Decimal 140 - 152
     * -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9, // Decimal 153 - 165
     * -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9, // Decimal 166 - 178
     * -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9, // Decimal 179 - 191
     * -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9, // Decimal 192 - 204
     * -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9, // Decimal 205 - 217
     * -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9, // Decimal 218 - 230
     * -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9, // Decimal 231 - 243
     * -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9 // Decimal 244 - 255
     */
    };

    // Indicates white space in encoding
    private final static byte WHITE_SPACE_ENC = -5;
    // Indicates equals sign in encoding
    private final static byte EQUALS_SIGN_ENC = -1;

    /** Defeats instantiation. */
    private Base64Util() {
    }

    /* ******** E N C O D I N G M E T H O D S ******** */

    /**
     * Encodes up to three bytes of the array <var>source</var> and writes the
     * resulting four Base64 bytes to <var>destination</var>. The source and
     * destination arrays can be manipulated anywhere along their length by
     * specifying <var>srcOffset</var> and <var>destOffset</var>. This method
     * does not check to make sure your arrays are large enough to accommodate
     * <var>srcOffset</var> + 3 for the <var>source</var> array or
     * <var>destOffset</var> + 4 for the <var>destination</var> array. The
     * actual number of significant bytes in your array is given by
     * <var>numSigBytes</var>.
     *
     * @param source
     *            the array to convert
     * @param srcOffset
     *            the index where conversion begins
     * @param numSigBytes
     *            the number of significant bytes in your array
     * @param destination
     *            the array to hold the conversion
     * @param destOffset
     *            the index where output will be put
     * @param alphabet
     *            is the encoding alphabet
     * @return the <var>destination</var> array
     * @since 1.3
     */
    private static byte[] encode3to4(byte[] source, int srcOffset, int numSigBytes,
            byte[] destination, int destOffset, byte[] alphabet) {
        // 1 2 3
        // 01234567890123456789012345678901 Bit position
        // --------000000001111111122222222 Array position from threeBytes
        // --------| || || || | Six bit groups to index alphabet
        // >>18 >>12 >> 6 >> 0 Right shift necessary
        // 0x3f 0x3f 0x3f Additional AND

        // Create buffer with zero-padding if there are only one or two
        // significant bytes passed in the array.
        // We have to shift left 24 in order to flush out the 1's that appear
        // when Java treats a value as negative that is cast from a byte to an
        // int.
        int inBuff = (numSigBytes > 0 ? ((source[srcOffset] << 24) >>> 8) : 0)
                | (numSigBytes > 1 ? ((source[srcOffset + 1] << 24) >>> 16) : 0)
                | (numSigBytes > 2 ? ((source[srcOffset + 2] << 24) >>> 24) : 0);

        switch (numSigBytes) {
        case 3:
            destination[destOffset] = alphabet[(inBuff >>> 18)];
            destination[destOffset + 1] = alphabet[(inBuff >>> 12) & 0x3f];
            destination[destOffset + 2] = alphabet[(inBuff >>> 6) & 0x3f];
            destination[destOffset + 3] = alphabet[(inBuff) & 0x3f];
            return destination;
        case 2:
            destination[destOffset] = alphabet[(inBuff >>> 18)];
            destination[destOffset + 1] = alphabet[(inBuff >>> 12) & 0x3f];
            destination[destOffset + 2] = alphabet[(inBuff >>> 6) & 0x3f];
            destination[destOffset + 3] = EQUALS_SIGN;
            return destination;
        case 1:
            destination[destOffset] = alphabet[(inBuff >>> 18)];
            destination[destOffset + 1] = alphabet[(inBuff >>> 12) & 0x3f];
            destination[destOffset + 2] = EQUALS_SIGN;
            destination[destOffset + 3] = EQUALS_SIGN;
            return destination;
        default:
            return destination;
        } // end switch
    } // end encode3to4

    /**
     * Encodes a byte array into Base64 notation. Equivalent to calling
     * {@code encodeBytes(source, 0, source.length)}
     *
     * @param source
     *            The data to convert
     * @since 1.4
     */
    public static String encode(byte[] source) {
        return encode(source, 0, source.length, ALPHABET, true);
    }

    /**
     * Encodes a byte array into web safe Base64 notation.
     *
     * @param source
     *            The data to convert
     * @param doPadding
     *            is {@code true} to pad result with '=' chars if it does not
     *            fall on 3 byte boundaries
     */
    public static String encodeWebSafe(byte[] source, boolean doPadding) {
        return encode(source, 0, source.length, WEBSAFE_ALPHABET, doPadding);
    }

    /**
     * Encodes a byte array into Base64 notation.
     *
     * @param source
     *            The data to convert
     * @param off
     *            Offset in array where conversion should begin
     * @param len
     *            Length of data to convert
     * @param alphabet
     *            is the encoding alphabet
     * @param doPadding
     *            is {@code true} to pad result with '=' chars if it does not
     *            fall on 3 byte boundaries
     * @since 1.4
     */
    public static String encode(byte[] source, int off, int len, byte[] alphabet, boolean doPadding) {
        byte[] outBuff = encode(source, off, len, alphabet, Integer.MAX_VALUE);
        int outLen = outBuff.length;

        // If doPadding is false, set length to truncate '='
        // padding characters
        while (doPadding == false && outLen > 0) {
            if (outBuff[outLen - 1] != '=') {
                break;
            }
            outLen -= 1;
        }

        return new String(outBuff, 0, outLen);
    }

    /**
     * Encodes a byte array into Base64 notation.
     *
     * @param source
     *            The data to convert
     * @param off
     *            Offset in array where conversion should begin
     * @param len
     *            Length of data to convert
     * @param alphabet
     *            is the encoding alphabet
     * @param maxLineLength
     *            maximum length of one line.
     * @return the BASE64-encoded byte array
     */
    public static byte[] encode(byte[] source, int off, int len, byte[] alphabet, int maxLineLength) {
        int lenDiv3 = (len + 2) / 3; // ceil(len / 3)
        int len43 = lenDiv3 * 4;
        byte[] outBuff = new byte[len43 // Main 4:3
                + (len43 / maxLineLength)]; // New lines

        int d = 0;
        int e = 0;
        int len2 = len - 2;
        int lineLength = 0;
        for (; d < len2; d += 3, e += 4) {

            // The following block of code is the same as
            // encode3to4( source, d + off, 3, outBuff, e, alphabet );
            // but inlined for faster encoding (~20% improvement)
            int inBuff = ((source[d + off] << 24) >>> 8) | ((source[d + 1 + off] << 24) >>> 16)
                    | ((source[d + 2 + off] << 24) >>> 24);
            outBuff[e] = alphabet[(inBuff >>> 18)];
            outBuff[e + 1] = alphabet[(inBuff >>> 12) & 0x3f];
            outBuff[e + 2] = alphabet[(inBuff >>> 6) & 0x3f];
            outBuff[e + 3] = alphabet[(inBuff) & 0x3f];

            lineLength += 4;
            if (lineLength == maxLineLength) {
                outBuff[e + 4] = NEW_LINE;
                e++;
                lineLength = 0;
            } // end if: end of line
        } // end for: each piece of array

        if (d < len) {
            encode3to4(source, d + off, len - d, outBuff, e, alphabet);

            lineLength += 4;
            if (lineLength == maxLineLength) {
                // Add a last newline
                outBuff[e + 4] = NEW_LINE;
                e++;
            }
            e += 4;
        }

        assert (e == outBuff.length);
        return outBuff;
    }

    /* ******** D E C O D I N G M E T H O D S ******** */

    /**
     * Decodes four bytes from array <var>source</var> and writes the resulting
     * bytes (up to three of them) to <var>destination</var>. The source and
     * destination arrays can be manipulated anywhere along their length by
     * specifying <var>srcOffset</var> and <var>destOffset</var>. This method
     * does not check to make sure your arrays are large enough to accommodate
     * <var>srcOffset</var> + 4 for the <var>source</var> array or
     * <var>destOffset</var> + 3 for the <var>destination</var> array. This
     * method returns the actual number of bytes that were converted from the
     * Base64 encoding.
     *
     *
     * @param source
     *            the array to convert
     * @param srcOffset
     *            the index where conversion begins
     * @param destination
     *            the array to hold the conversion
     * @param destOffset
     *            the index where output will be put
     * @param decodabet
     *            the decodabet for decoding Base64 content
     * @return the number of decoded bytes converted
     * @since 1.3
     */
    private static int decode4to3(byte[] source, int srcOffset, byte[] destination, int destOffset,
            byte[] decodabet) {
        // Example: Dk==
        if (source[srcOffset + 2] == EQUALS_SIGN) {
            int outBuff = ((decodabet[source[srcOffset]] << 24) >>> 6)
                    | ((decodabet[source[srcOffset + 1]] << 24) >>> 12);

            destination[destOffset] = (byte) (outBuff >>> 16);
            return 1;
        } else if (source[srcOffset + 3] == EQUALS_SIGN) {
            // Example: DkL=
            int outBuff = ((decodabet[source[srcOffset]] << 24) >>> 6)
                    | ((decodabet[source[srcOffset + 1]] << 24) >>> 12)
                    | ((decodabet[source[srcOffset + 2]] << 24) >>> 18);

            destination[destOffset] = (byte) (outBuff >>> 16);
            destination[destOffset + 1] = (byte) (outBuff >>> 8);
            return 2;
        } else {
            // Example: DkLE
            int outBuff = ((decodabet[source[srcOffset]] << 24) >>> 6)
                    | ((decodabet[source[srcOffset + 1]] << 24) >>> 12)
                    | ((decodabet[source[srcOffset + 2]] << 24) >>> 18)
                    | ((decodabet[source[srcOffset + 3]] << 24) >>> 24);

            destination[destOffset] = (byte) (outBuff >> 16);
            destination[destOffset + 1] = (byte) (outBuff >> 8);
            destination[destOffset + 2] = (byte) (outBuff);
            return 3;
        }
    } // end decodeToBytes

    /**
     * Decodes data from Base64 notation.
     *
     * @param s
     *            the string to decode (decoded in default encoding)
     * @return the decoded data
     * @since 1.4
     */
    public static byte[] decode(String s) throws Exception {
        byte[] bytes = s.getBytes();
        return decode(bytes, 0, bytes.length);
    }

    /**
     * Decodes data from web safe Base64 notation. Web safe encoding uses '-'
     * instead of '+', '_' instead of '/'
     *
     * @param s
     *            the string to decode (decoded in default encoding)
     * @return the decoded data
     */
    public static byte[] decodeWebSafe(String s) throws Exception {
        byte[] bytes = s.getBytes();
        return decodeWebSafe(bytes, 0, bytes.length);
    }

    /**
     * Decodes Base64 content in byte array format and returns the decoded byte
     * array.
     *
     * @param source
     *            The Base64 encoded data
     * @return decoded data
     * @since 1.3
     * @throws Base64DecoderException
     */
    public static byte[] decode(byte[] source) throws Exception {
        return decode(source, 0, source.length);
    }

    /**
     * Decodes web safe Base64 content in byte array format and returns the
     * decoded data. Web safe encoding uses '-' instead of '+', '_' instead of
     * '/'
     *
     * @param source
     *            the string to decode (decoded in default encoding)
     * @return the decoded data
     */
    public static byte[] decodeWebSafe(byte[] source) throws Exception {
        return decodeWebSafe(source, 0, source.length);
    }

    /**
     * Decodes Base64 content in byte array format and returns the decoded byte
     * array.
     *
     * @param source
     *            The Base64 encoded data
     * @param off
     *            The offset of where to begin decoding
     * @param len
     *            The length of characters to decode
     * @return decoded data
     * @since 1.3
     * @throws Base64DecoderException
     */
    public static byte[] decode(byte[] source, int off, int len) throws Exception {
        return decode(source, off, len, DECODABET);
    }

    /**
     * Decodes web safe Base64 content in byte array format and returns the
     * decoded byte array. Web safe encoding uses '-' instead of '+', '_'
     * instead of '/'
     *
     * @param source
     *            The Base64 encoded data
     * @param off
     *            The offset of where to begin decoding
     * @param len
     *            The length of characters to decode
     * @return decoded data
     */
    public static byte[] decodeWebSafe(byte[] source, int off, int len) throws Exception {
        return decode(source, off, len, WEBSAFE_DECODABET);
    }

    /**
     * Decodes Base64 content using the supplied decodabet and returns the
     * decoded byte array.
     *
     * @param source
     *            The Base64 encoded data
     * @param off
     *            The offset of where to begin decoding
     * @param len
     *            The length of characters to decode
     * @param decodabet
     *            the decodabet for decoding Base64 content
     * @return decoded data
     */
    public static byte[] decode(byte[] source, int off, int len, byte[] decodabet) throws Exception {
        int len34 = len * 3 / 4;
        byte[] outBuff = new byte[2 + len34]; // Upper limit on size of output
        int outBuffPosn = 0;

        byte[] b4 = new byte[4];
        int b4Posn = 0;
        int i = 0;
        byte sbiCrop = 0;
        byte sbiDecode = 0;
        for (i = 0; i < len; i++) {
            sbiCrop = (byte) (source[i + off] & 0x7f); // Only the low seven
                                                       // bits
            sbiDecode = decodabet[sbiCrop];

            if (sbiDecode >= WHITE_SPACE_ENC) { // White space Equals sign or
                                                // better
                if (sbiDecode >= EQUALS_SIGN_ENC) {
                    // An equals sign (for padding) must not occur at position 0
                    // or 1
                    // and must be the last byte[s] in the encoded value
                    if (sbiCrop == EQUALS_SIGN) {
                        int bytesLeft = len - i;
                        byte lastByte = (byte) (source[len - 1 + off] & 0x7f);
                        if (b4Posn == 0 || b4Posn == 1) {
                            throw new Exception("invalid padding byte '=' at byte offset " + i);
                        } else if ((b4Posn == 3 && bytesLeft > 2) || (b4Posn == 4 && bytesLeft > 1)) {
                            throw new Exception(
                                    "padding byte '=' falsely signals end of encoded value "
                                            + "at offset " + i);
                        } else if (lastByte != EQUALS_SIGN && lastByte != NEW_LINE) {
                            throw new Exception("encoded value has invalid trailing byte");
                        }
                        break;
                    }

                    b4[b4Posn++] = sbiCrop;
                    if (b4Posn == 4) {
                        outBuffPosn += decode4to3(b4, 0, outBuff, outBuffPosn, decodabet);
                        b4Posn = 0;
                    }
                }
            } else {
                throw new Exception("Bad Base64 input character at " + i + ": " + source[i + off]
                        + "(decimal)");
            }
        }

        // Because web safe encoding allows non padding base64 encodes, we
        // need to pad the rest of the b4 buffer with equal signs when
        // b4Posn != 0. There can be at most 2 equal signs at the end of
        // four characters, so the b4 buffer must have two or three
        // characters. This also catches the case where the input is
        // padded with EQUALS_SIGN
        if (b4Posn != 0) {
            if (b4Posn == 1) {
                throw new Exception("single trailing character at offset " + (len - 1));
            }
            b4[b4Posn++] = EQUALS_SIGN;
            outBuffPosn += decode4to3(b4, 0, outBuff, outBuffPosn, decodabet);
        }

        byte[] out = new byte[outBuffPosn];
        System.arraycopy(outBuff, 0, out, 0, outBuffPosn);
        return out;
    }
}
